Some 43 surficial sediment samples of the Semnan Province and NE of the Isfahan Province were collected. Powdered sand sized fraction of these samples were analyzed by XRF method for major elements. Some 8 selected samples along with 8 extra samples collected from more conspicuous rock units exposed around the periphery of these study areas were also analyzed by ICP-MS for REE in the laboratory of the Geological Survey of Iran (Karaj Division). A variety of rock types including silicic, to basic intrusive, subvolcanics and extrusive rocks exposed in these areas. Geochemical interpretations revealed that surficial sediments of both study areas stemmed from intermediate igneous rocks and mafic rocks for the NE Isfahan province as well. Samples of the Semnan Province show PCM (Passive Continental Margin), while those of the NE Isfahan are more complex and fall in the realm of OIS (Oceanic Island Arc), CIA (Continental Island Arc), and ACM Active Continental Margin) as well. The REE and trace element composition of 8 sediment samples and 8 rock samples (proportionally equal quantities for both study areas), show enriched LREE, high LREE/HREE ratio and depleted Eu anomaly for both areas. These evidences support an acidic igneous rocks origin (possibly tuffs of the Karaj Formation) for the Semnan area. Although for the NE of Isfahan Province, it is slightly divers. Here, igneous acidic to intermediate igneous rocks, ultramafic and ophiolites of the Anarak-Khour area, ophiolite complexes exposed along major faults (e.g. Nain- Dehshir-Baft) are invoked for the plausible provenance of the sediments.
